The present invention relates to oil and gas industry. It involves equipment for a new abrasive hydrojet perforation which offers an effective means to communicate the wellbore with the target formation and to achieve more effective completion due to an increase of flow area, bypassing the damage in a near-wellbore zone and reduction of the compressive stresses. The invention represents a new system for treatment of a near-well zone of producing formation with a combination of chemical treatment.
It is known that the flow from productive zones can be increased by slotting and chemical treatment. Slotting allows redistribution of the mechanical stresses in the near well zone, while chemical treatment allows increased productivity of the wells. However, the first method is very labor consuming and requires high costs. In order to shot three feet of the productive interval some time it is necessary to spend up to three hours of pumping unit operation, which is an expensive operation. The chemical action also treats the near well zone, but it requires a primary opening of the formation and does not remove a zone of support pressure which is a main reason of locking of the passages for fluid flow into the well. The first method is very efficient and increases the productivity of wells on average several times, however it is expensive. In order to provide maximum effectiveness or completely restore the potential productivity of wells, it is usually necessary to provide a subsequent treatment with formation-treating reagents.
The method and system disclosed in SU1167925 is a combined solution for the increase of productivity, which includes slotting of the well and cyclic acid formation treatment. The slotting is performed in accordance with known “classic” recommendations in order to obtain a maximum possible effect, while the cyclic acid treatment is performed also in accordance with the known method described in the above mentioned documents, for a depth which is not less than 5 diameters of the well, so as to attempt to completely use its possibilities without the consideration of the results of slotting or control of the results of each cycle. The cyclical “periodic” treatment of a well was performed by a reagent solution whose volume was determined from a mass and porosity of rock adjoining a shaft of the well, at a distance of approximately two diameters from the well. Each cycle of treatment is performed by pressing of a calculated volume of solution into the formation to be treated, which is preliminary limited from above and from below by packers. The treatment in some sense is performed blindly, the results were evaluated in accordance with a change of productivity of the well. The cycles of treatment continued until the time when repetition did not lead to a change in productivity.
It has been shown from practice that this method and system which include a complete slotting with a subsequent complete treatment with technological reagents has a universal action of the formation and provides an increase of well productivity, an equalization of a profile of advancement of a front of water pumped into a formation for maintaining of the formation pressure, a increase of the oil yield of the formation. Because of these advantages this method has been widely utilized. It also has been used during exploration and drilling of new wells. Moreover, it was made possible with this method to explore and efficiently use wells in low-production formations of Western Siberia in which the oil flow is less than 30 bbl per day. This method therefore is efficient. However, this method, similarly to the other methods has a limitation as to its possibility and efficiency. It is expensive, labor consuming and does not guarantee obtaining of the maximum possible increase of well productivity. The method is used without consideration of negative action of elevated stress concentrations, which are formed near the wellbore.
It is known that the maximum stresses in the near well zone are generated within one diameter of the well or approximately 0.6 ft., and the maximum stress directly adjoins the walls of the well (FIG. 1). The plastic zone in this case can be not considered, since in accordance with the calculation its width at the depth of 10,000 ft. is only 0.03 ft.. It is also known that during the process of drilling of wells, even after carrying out of slot slotting, a zone of support pressure remains near it. The slot removes only a part of these stresses, which is equivalent to a reduction of depth of the well approximately 1.5 times. During slotting at the depth of 10,000 ft. it is equivalent to a reduction of stresses to the depth of 6,600 ft.. However, the mode and parameters of acid treatment (or treatment with other reagents, such as technological compositions) nowadays are determined without consideration of negative influence of the remaining stresses near the well. The zone of support pressure, which remains around the well, is not taken into consideration and parameters of treatment with technological compositions are calculated from the condition of action of a uniform supply of active technological solution per volume unit of a formation.
However, experimental observations and analytical investigations showed that the influence of zone of support pressure near the well is significant. If this influence is not taken into consideration, false conclusions can be made with respect to the productivity of the wells. Based on the results of the treatment, it is considered that a low oil yield from a formation can be explained by a week natural permeability of the formation itself, while a real cause is the reduction of permeability only within limits of the zone of support stresses, caused by stress concentration beyond the wellbore.